Green Synthesis and Characterization of Ag Nanoparticles Using Leaf Extract of Maerua Angolensis for Antimicrobial Studies

Nanotechnology has emerged as one of the most transformative fields in modern science, particularly in the synthesis and application of nanoscale materials. Nanoparticles, typically ranging from 1–100 nm in size, exhibit unique physicochemical properties such as high surface area-to-volume ratio, enhanced catalytic activity, and improved optical behavior compared to their bulk counterparts [1]. Among these, noble metal nanoparticles especially silver (Ag) and copper (Cu) have gained considerable attention due to their remarkable antimicrobial, antioxidant, and catalytic properties.

Conventional methods for synthesizing nanoparticles, including chemical reduction and physical approaches, often involve toxic reagents, high energy consumption, and environmentally hazardous by-products. These drawbacks have necessitated the development of eco-friendly and sustainable alternatives. Green synthesis, which utilizes biological entities such as plant extracts, microorganisms, and biomolecules, has emerged as a viable and environmentally benign approach [17]. Plant-mediated synthesis is particularly advantageous due to its simplicity, cost-effectiveness, scalability, and the presence of phytochemicals that act as both reducing and stabilizing agents. Various plants contain bioactive compounds such as flavonoids, phenolics, alkaloids, terpenoids, and proteins, which facilitate the reduction of metal ions into nanoparticles while simultaneously capping them to enhance stability.

1.1 Green Synthesis

Green Chemistry has been one of the most interesting sciences of the past few years as an alternative to traditional chemistry. This is mainly due to the energy crisis and its constraints particularly in developing countries. Therefore, serious consideration given to the development of green chemistry has resulted in significant efforts in the multidisciplinary and interdisciplinary scientific fields [12].

[18] Reported that convergence of Nano-meter-size-scale technologies has created the new field of Nanoscience, including nanotechnology and Nanobiotechnology. This relatively new field focuses on the creation and use of materials at the nanometer scale for advanced biotechnology. Thus nanoscience in green chemistry has opened the door to multiple opportunities by enabling variable numbers of chemical, physical, biochemical, and biophysical transformations in a reliable manner. In this respect, the use of nanoparticles has made the fields of catalysis, synthesis, and enzyme immobilizations as well as molecular interactions, much easier, rapid and controllable.

1.2 Maerua angolensis

Maerua angolensis is a deciduous tree belonging to the Family Capparaceae. The genus name "Maerua" means "drooping" in reference to the drooping foliage. As reported by [4], its common English name is "bead bean". Maerua angolensis is a shrub or small to medium-sized and rounded tree which can grow up to 10 metres high and is widely distributed in continental tropical Africa. The plant materials have been used for numerous ethno medicinal uses across the region. The bark on young stems is purplish to yellowish in colour with light grey corky lenticels, and smooth and grey to rough and dark grey, peeling off in small flakes on older stems. The leaves locally known as 'Leggel bale' in Fulfulde Language are used to treat diabetes in parts of northern Nigeria; and the root and stem bark used as an aphrodisiac, and to cure diarrhoea and epilepsy in Tanzania.

2. MATERIALS AND METHODS

2.1 Materials

2.1.1 Reagents and Chemicals

Methanol, Ciprofloxacin, AgCl, dimethyl sulphoxide (DMSO), Nutrient Agar, sterilized petridish, Hinton sensitivity agar fungal culture plate, Plant extracts (leaf) buffer solution.

2.1.2 Apparatus and Analytical Tools

Conical flask different sizes, Filter paper, Rotary evaporator, Burette, Micropipette, XRD, FTIR (Agilent Technology), SEM.

2.2 Methods

2.2.1 Sample Collection and Authentication

The leaves of Maerua angolensis was collected at Potiskum L.G.A of Yobe State. The plant material was identified and authenticated by a specialist in the herbarium of Department of Botany, given a voucher number GSUH 240, Gombe State University, Gombe, Nigeria.

2.2.2 Sample Preparation

The fresh leaves of Maerua angolensis was collected and washed with distilled water to remove dirty particles and sliced using a stainless-steel knife, and air-dried under a sheath over a period of two weeks and ground using mortar and pestle to obtain fine powder particles used for the analysis [6].

2.2.3 Extract Preparation

The sample preparation was done using a slightly modified literature of [14], where 30 g of the leaf extract was weighed and dispersed into 200 ml distilled water in a 500 ml glass beaker and boiled at 80°C for 30 minutes and allowed to cool and filtered using filter paper. The filtrate was used for the synthesis of nanocomposite.

2.2.4 Preparation of Reagent: AgCl Solution

0.01 M solution of the metal was prepared by dissolving 1.632 g of the salt into 100 ml volumetric flask and distilled water was added to the mark [15].

2.3 Synthesis of Silver Nanoparticles (AgNPs)

By using a slightly modified method of [18], for the synthesis of the metal, leaf extract was prepared. The AgCl solution was added drop wise concordantly into the plant extract in a ratio of 1:9 (that is 10 ml extract and 90 ml metallic precursor) with constant stirring at 60°C for 60 minutes using magnetic stirrer. Within the first 15 minutes the color change was observed which indicated the formation of nanoparticles. The mixture was allowed to settle for 24 hours (one day) after which it was decanted and dried. The collected nanoparticles at 100°C for 2 hours were then ground into powder for further analysis.

2.4 Characterization

Characterization was done on synthesized nanoparticles using various analytical tools such as UV-visible (200 nm to 800 nm), SEM, FT-IR, and XRD.

2.4.1 UV-Visible Spectrophotometry Analysis

UV-Visible spectroscopy analysis was done to confirm the formation of nanoparticles and observe the extract plasmon vibration and excitation. The wavelength was varied at regular wavelength of 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, and 800 nm respectively.

3. RESULTS AND DISCUSSION

3.1 UV-Visible Spectrophotometry Analysis

Table 1: UV-Visible Spectrophotometry Analysis Results for the Leaf Extract

Sample	Absorbance
Maerua angolensis leaf	450nm
AgNPs	430nm

 

 

 

Figure 1: UV-Visible Spectrum of the Maerua angolensis Leaf Extract

 

 

Figure 2: UV-Visible Spectrum of Silver Nanoparticles (AgNPs)

 

 

Figure 3: FTIR Spectra of Maerua angolensis Leaf Extract

Table 3: FT-IR of AgNPs using Maerua angolensis Leaf Extract

FT-IR Peak (cm⁻¹)	Functional Group	Phytochemical Class
3283.3	Hydroxyl(OH)/Amine (N-H)	Phenols, flavonoids, proteins
2849.5	Aldehyde/Alkane (C-H)	Fatty acids, aldehydes
1720.2	Carbonyl (C=O)	Esters, aldehydes, ketones
1101.4	Alcohol/Ether (C-O)	Glycosides, carbohydrates

 

 

 

Figure 4: FT-IR Analysis of Silver Nanoparticles (AgNPs)

 

 

Figure 5: SEM Image of Maerua angolensis Leaf Extract AgNPs

The SEM image of Maerua angolensis leaf extract AgNPs shows a heterogeneous, rough and relatively compact surface with irregularly distributed granular features and some degree of aggregation. The observed aggregation may result from strong inter particle interactions and the high surface energy of nanoparticles, as well as drying during SEM sample preparation. Plant-derived biomolecules can also influence growth, stabilization and the final morphology of AgNPs [2].

3.4 X-Ray Diffraction (XRD) Analysis

XRD analysis was done to find out the average crystalline size. The Debye Scherer equation was used to calculate the average crystalline size:

D=Kλ/βCOSθ

 

Where: D= Particles size = 0.94

K= Constant volume

λ= X-ray wavelength (0.154nm)

β=Line broadening at half the maximum intensity

θ= Braggs angle (in degree).

The plant extract against Aspergillus Niger showed an increase in fungal inhibition with an increase in the concentration of the plant extract, showing the high rate of inhibition at 500 µg/ml. The Candida showed an increase in the fungal growth as the concentration increases and the highest inhibition was observed at 500 µg/ml. This shows that as the concentration increases, the zone of inhibition increases. The silver nanoparticles (AgNPs) against Aspergillus Niger showed an increase in fungal growth inhibition with increase in concentration of the synthesized drug (nanoparticles). It showed highest fungi inhibition rate at concentration 300 µg/ml but decreased in concentration 400 µg/ml and 500 µg/ml respectively. This decrease depends on the type of fungi in question. Each fungi has its own activity and resistance to the drug used. In relation to literature of [20].

CONCLUSION

The green synthesis of silver nanoparticles (AgNPs) using aqueous leaf extract of Maerua angolensis has been successfully achieved, demonstrating an eco-friendly, cost-effective, and sustainable approach to nanomaterial synthesis. The formation of AgNPs was confirmed by UV-Visible spectroscopy, showing a characteristic surface plasmon resonance peak at 430 nm, indicative of nanoparticle formation. FT-IR analysis revealed the presence of various functional groups including hydroxyl, carbonyl, amine, and aromatic groups from phytochemicals such as phenols, flavonoids, proteins, and alkaloids, which played dual roles as reducing and stabilizing agents during the synthesis process.

XRD analysis confirmed the crystalline nature of the AgNPs with face-centered cubic (FCC) structure, showing prominent diffraction peaks corresponding to (111), (200), (220), and (311) planes, with an average crystallite size of 32 nm. SEM analysis revealed heterogeneous, rough, and compact surface morphology with some aggregation, which is typical for biologically synthesized nanoparticles.

The antimicrobial studies demonstrated that both the plant extract and synthesized AgNPs exhibited significant antibacterial and antifungal activities against the tested microorganisms. The AgNPs showed enhanced antimicrobial activity compared to the plant extract alone, with concentration-dependent inhibition zones. The highest antibacterial activity was observed against Pseudomonas aeruginosa (18 mm at 500 µg/ml), while the most significant antifungal activity was recorded against Candida (22 mm at 500 µg/ml). The enhanced antimicrobial activity of AgNPs can be attributed to their small size, large surface area-to-volume ratio, and the synergistic effect of silver ions with phytochemicals present on the nanoparticle surface.

This study successfully demonstrates that Maerua angolensis leaf extract serves as an excellent bio-reductant and stabilizing agent for the green synthesis of AgNPs with promising antimicrobial properties. The synthesized nanoparticles showed potential as effective antimicrobial agents against both Gram-positive and Gram-negative bacteria as well as fungal pathogens. The findings suggest that these biosynthesized AgNPs could be developed as alternative therapeutic agents for the treatment of infectious diseases, particularly in the face of increasing antimicrobial resistance. Further studies are recommended to investigate the mechanism of antimicrobial action, cytotoxicity, and in vivo efficacy of these nanoparticles for potential pharmaceutical and biomedical applications.

REFERENCES

1. Ahmed, S., Ahmad, M., Swami, B. L., & Ikram, S. (2016). A review on plants extract mediated synthesis of silver nanoparticles for antimicrobial applications: A green expertise.                                   Journal of Advanced Research, 7(1), 17–28. https://doi.org/10.1016/j.jare.2015.02.007
2. Banerjee, P., Satapathy, M., Mukhopahayay, A., & Das, P. (2014). Synthesis, characterization, antimicrobial property and toxicity analysis. Leaf extract mediated green synthesis of        silver nanoparticles from widely available Indian plants. Bioresources and Bioprocessing.            https://doi.org/10.1186/s40643-014-0003
3. Camargo, P. H., Satyanarayana, K. G., & Wypych, F. (2009). Nanocomposites: Synthesis, structure, properties and new application opportunities. Materials Research, 12(1), 1-39.
4. Dharani, N. (2019). Field Guide to Common Trees & Shrubs of East Africa. Struik Nature.(3^rd  ed.). Struik Nature
5. Fatemeh, B., Alireza, A., & Sayed, A. H. (2018). Green synthesis characterization and           antimicrobial activity of silver nanoparticles from root extract of Tapidium draba weed.     Green Chemistry Letters and Reviews, 10(4), 324-330.
6. Igwe, O. U., & Ekebo, E. S. (2018). Bio fabrication of cobalt nanoparticles using leaf extract of       Chromolaena odorata and their potential antibacterial application. Research Journal of             Chemical Sciences, 8(1), 11-17.
7. Iliya, H. A., Boakye-Gyasi, E., Adongo, W. D., Ampadu, F. A., & Woode, E. (2014).     Antinociceptive activity of various solvent extracts of Maerua angolensis DC stem bark            in rodents. The Journal of Psychopharmacology, 3(1), 1-8.
8. Iravani, S. (2011). Green synthesis of metal nanoparticles using plants. Green Chemistry, 13(10),           2638–2650. https://doi.org/10.1039/C1GC15386B
9. Iravani, S., Korbekandi, H., Mirmohammadi, S. V., & Zolfaghari, B. (2014). Synthesis of silver           nanoparticles: Chemical, physical and biological methods. Research in Pharmaceutical    Sciences, 9(6), 385–406.
10. Lamayi, D. W., Mela, Y., Yahaya, P. N., & Shehu, Z. (2021). Synthesis, characterization and        catalytic application of magnetic iron nanoparticles (Fe₃O₄) in biodiesel production from      Mahogany (Khaya senegalensis) seed oil. Online Journal of Chemistry, 1, 85-94.   https://doi.org/10.31586/ojc.149
11. Manas, I. Z. (2012). Mixing and Compounding of Polymers: Theory and Practice. Carl Hanser          Research Spring, Co. LTD. PP.5-15.
12. Matlack, A. S. (2010). Introduction to Green Chemistry (2nd ed.). CRC Press: New      York/London. https://doi.org/10.1201/97814 p1-600.
13. Nasiru, Y. P., Adamu, A., Wilson, L. D., & Usman, Y. M. (2023). Green synthesis and           characterization of iron nanoparticles from the leaf extract of Khaya senegalensis         (Mahogany) and its antimicrobial activity. Letters in Applied Nano Bioscience, 12(3), 86.
14. Nasiru, Y. P., Khadija, A. Y., Adamu, A., & Yakong, D. M. (2022). Green synthesis and       characterization of cobalt, iron and copper nanoparticles derived from the stem-bark          extract of Khaya senegalensis (Mahogany) and its antimicrobial activity. Online Journal    of Chemistry, 1.
15. Pindiga, N. Y., Abubakar, A., Danbature, W. L., & Mohammed, U. Y. (2023). Green synthesis   and characterization of iron nanoparticles from the leaf extract of Khaya senegalensis and          its antimicrobial activity. Journal of Applied Nano-Bioscience, 12(3), 86, pp. 1-9.
16. Sharma, D., Kanchi, S., & Bisetty, K. (2019). Biogenic synthesis of nanoparticles: A review. Arabian Journal of Chemistry, 12(8), 3576–3600.
17. Singh, P., Kim, Y. J., Zhang, D., & Yang, D. C. (2018). Biological synthesis of nanoparticles                   from plants and microorganisms. Trends in Biotechnology, 34(7), 588–599.
18. Wilson, L. D., Yoro, M., Nasiru, Y. P., & Zaccheus, S. (2021). Synthesis, characterization and        catalytic application of magnetic iron nanoparticles (Fe₃O₄) in biodiesel production from      Mahogany (Khaya senegalensis) seed oil. Online Journal of Chemistry, 2021, 1, 85-94.
19. Yahaya, N. P., Lamayi, W. D., & Bawaji, S. M. (2023). Green synthesis and characterization of           bimetallic (Ag-Cu) nanoparticles from leaf extract of Celtis integrifolia and its antimicrobial activity. Journal of Nanoanalysis, 10(1), pp. 439-451.
20. Zaccheus, S., Danbature, W. L., Maisanda, A. S., & Musa, M. S. (2018). Synthesis,      characterization and antibacterial activity of Kaolin gum Arabic nanocomposite on             Escherichia coli and Pseudomonas aeruginosa. Research Journal of Nanoscience and Engineering, 2(2), 23-29.